1. Field of the Invention
The present invention relates to a method of analyzing a lighting environment for use in simulating lighting or the like in a certain room by the use of a computer, and also to an analyzer for effecting this method.
2. Description of the Prior Art
In installing lighting fixtures in a room, it is desired to quantitatively analyze a lighting environment, prior to the installation, by computing the illuminance, luminance or the like at various locations in the room. In applications where such an analysis is performed, reflected light from walls as well as direct light from light sources should be taken into consideration.
Conventionally, a computation wherein the reflected light is taken into consideration is carried out with the use of a radiosity algorithm (see "A Progressive Refinement Approach to Fast Radiosity Image Generation" Michael F. Cohen etal., Computer Graphics, Vol. 22, No. 4, Aug. 1988 (SIGGRAPH '88 Conference Proceeding), pp. 75-84).
In this algorithm, ceilings, side walls, floors and any other structural elements constituting a room are initially divided into a large number of surface areas or patches. As a matter of course, an illuminating light source is contained in at least one of the surface areas or patches.
In view of this fact, of the patches, attention should first be paid to those patches radiating the most light energy, i.e., those patches containing illuminating light sources. Light is radiated from these patches in all directions. In determining the rate of light radiated from one patch which arrives at other patches, form-factors are initially computed based on the angle of radiation, the size of the patches and the like. A method of computing the form-factors is based on the number of lines emitted from one point (on the patch containing an illuminating light source) which arrive at other patches.
FIG. 1 is a flowchart indicating the procedure for computing the form-factors.
The angle of radiation of a light ray is computed at step S1. The luminous intensity of the light ray radiated at the computed angle is computed at step S2. The patch at which the light ray arrives is searched at step S3 based on the angle of radiation. The luminous intensity on the patch is computed at step S4 (the resultant value is cumulatively added). Step S5 determines as to whether computations have been terminated with respect to all lines emitted from said one point. If some lines remain to which computations have not been performed yet, the procedure returns to step S1 to compute the luminous intensity of light rays passing through those lines. If the radiation of light rays is terminated at all angles, the quantity of light radiated from said one point which arrives at each patch is computed at step S6.
Subsequently, of all the patches except the patch containing a light source, a patch having a largest luminous intensity is searched. This patch is regarded as a new light source and as a complete diffusing surface. Then, light is radiated from this patch in all directions, thereby gradually increasing the luminous intensity of each patch. In this way, the quantity of all light rays received by each patch is computed with accuracy.
For the above computations, a computer simulation is generally available wherein the illuminance of walls, floors, ceilings, furnitures, household stuffs, and other objects is computed by tracing not only direct light rays from an illuminator and natural lighting but also light rays reflected several times by these structural elements. The above-mentioned computer simulation is capable of not only performing a simulation by the input of a variety of conditions, but also comparing simulation results by varying the input conditions. Because of this, the computer simulation can reduce the time required for computations with a higher accuracy, and is, therefore, very effective when it is extensively put to practical use.
With reference to FIGS. 2 to 4, an exemplified conventional method and apparatus for analyzing a light environment is hereinafter discussed wherein a computer simulation is employed.
FIG. 3 is a flowchart indicating the procedure of the conventional method.
Step S11 is a tracing block and mesh coordinate input process wherein the entire internal space defined in a room or lighting environmental space to be analyzed are initially divided into a plurality of tracing blocks or hemi-cubes so that a computer can readily trace trails of light rays reflecting in the room. In FIG. 2, reference numeral 20 denotes one of the tracing blocks. In this process, coordinates of all the X-Y, Y-Z, and Z-X planes are inputted into a tracing block and mesh coordinate input means 1 shown in FIG. 4. The X-Y, Y-Z, and Z-X planes finely divide the surface of all objects such as walls, floors, ceilings, furnitures, and any other household stuffs constituting the entire internal surface of the room into tracing meshes each having an arbitrary rectangular configuration. In FIG. 2, reference numerals 21 denote the tracing meshes. Then, the tracing blocks 20 and the tracing meshes 21 are stored in a memory means 2 shown in FIG. 4. Thereafter, the procedure proceeds to step S12.
Step S12 is a physical property input process wherein, for each tracing mesh 21 obtained at step S11, the physical properties associated with light reception and reflection of an object having the tracing mesh 21 are inputted into and stored in the memory means 2.
Step S13 is a maximum reflective surface searching process wherein a maximum reflective surface searching means 3 shown in FIG. 4 searches the tracing mesh 21 having the maximum quantity of reflected light from among all the tracing meshes 21 obtained at step S11. As a matter of course, the target mesh is a tracing mesh containing a light source at first or a tracing mesh of which the product of the total quantity of light received thereby and the reflectance thereof is maximum at the time light radiated from the light source is being reflected. After the search operation completes, the procedure proceeds to step S14.
Step S14 is a light ray radiation angle determining process wherein a light ray radiation angle determining means 4 shown in FIG. 4 determines the radiation angles of a plurality of light rays radiated from the tracing mesh 21 searched at step S13 according to the quantity of light thereof. When the tracing mesh 21 contains a light source, the radiation angles are determined based on the luminous intensity distribution standards wherein the luminous intensity differs according to the direction of radiation and wherein the luminous intensity is highest in the frontward direction and is gradually reduced as the direction of radiation departs from the frontward direction. On the other hand, when the tracing mesh 21 is a reflective surface, the radiation angles are determined so that light rays may be reflected uniformly in all directions.
Step S15 is a luminous intensity computing process wherein a luminous intensity computing means 5 shown in FIG. 4 computes the luminous intensity of radiated light according to the direction of radiation. When the tracing mesh 21 having the maximum quantity of reflected light contains the light source, the luminous intensity of radiated light is computed based on the luminous intensity distribution standards. When the tracing mesh 21 is the reflective surface, the luminous intensity of radiated light is computed so that the reflection angles may follow Lambert's cosine law.
Step S16 is a form-factor operation process for each tracing mesh 21 wherein, when a plurality of light rays having respective radiation angles obtained at step S14 and respective luminous intensities obtained at step S15 are-radiated from the tracing mesh 21 which has the maximum quantity of reflected light and has been searched at step S13, a form-factor operation means 6 shown in FIG. 4 searches a receiving tracing mesh 21 at which each light ray arrives successively through the tracing blocks 20 obtained at step S11 and computes the quantity of light received by the receiving tracing mesh 21. Also, the formfactor operation means 6 performs operations to obtain the ratio between the sum of the quantity of light received by each tracing mesh 21 and the total sum of the quantity of light received by all the tracing meshes 21. This ratio is the so-called form-factor for each tracing mesh 21.
Step S17 is a received light quantity operation process wherein a received light quantity operation means 7 shown in FIG. 4 performs operations to obtain the quantity of light received by each tracing mesh 21 based on the quantity of reflected light of the tracing mesh 21 having the maximum quantity of reflected light and the form factor of each tracing mesh 21 obtained at step S16.
Step S18 is an adding process wherein an adding means 8 shown in FIG. 4 cumulatively adds the quantity of light received by each tracing mesh 21 which has been obtained at step S17.
Step S19 is a reflected light quantity operation process wherein a reflected light quantity operation means 9 shown in FIG. 4 performs operations to obtain the quantity of reflected light of each tracing mesh 21 based on the cumulative quantity of light received thereby and the reflectance thereof.
Step S20 is a judging process wherein a comparing means 10 shown in FIG. 4 compares the total sum of the quantity of reflected light of all the tracing meshes 21 at that time with a predetermined quantity of light (normally about 5% of the total quantity of light radiated from the light source). When the total sum is not less than the predetermined quantity of light, the procedure returns to step S13. In contrast, when the former is less than the latter, the operations end.
In the above-mentioned conventional construction, all internal surfaces forming a lighting environmental space to be analyzed are divided into the tracing blocks 20 10 by a plurality of X-Y, Y-Z, and Z-X planes, and all surfaces of each of the aforementioned objects constituting the entire internal surface of the lighting environmental space are finely divided by additional X-Y, Y-Z, and Z-X planes into the tracing meshes 21 each having an arbitrary rectangular configuration, as shown in FIG. 2. By doing so, the computer can readily trace trails of light rays which are being reflected inside the room. In this construction, however, wall surfaces are initially divided into large tracing meshes and are further divided into small tracing meshes by the additional X-Y, Y-Z, and Z-X planes due to the presence of furnitures. Because of this, some tracing meshes of the wall surfaces take the form of relatively small tracing meshes 21 or flat tracing meshes 21 having a large aspect ratio under the influence of the configuration of the furnitures. However, it is not necessary to divide the wall surfaces into such small tracing meshes.
When the small tracing meshes 21 are used, operations required to obtain the trails of light rays, the quantity of reflected light, and the quantity of light received by each tracing mesh need a lot of time, thus resulting in lack of practicability.
In operations to obtain the quantity of reflected light of the flat tracing meshes 21 having a large aspect ratio, because the computer regards them as containing a point light source irrespective of the configuration thereof, the operation result is substantially the same as that of a case where tracing meshes 21 having an aspect ratio of one contain a light source, thereby causing errors.
In operations to obtain the quantity of light received by the flat tracing meshes 21 having a large aspect ratio, the computer is not free from errors. Accordingly, the presence of the flat tracing meshes 21 having a large aspect ratio enlarges the errors.
In addition, walls, ceilings, floors and any other structural elements constituting a room have all hitherto been regarded as complete diffusing surfaces.
Actually, however, some rooms are provided with a mirror or mirrors or other surfaces effecting mirror reflection. Also, there may be some surfaces effecting both diffusion reflection and mirror reflection.
There have been proposed no practical methods capable of accurately simulating a lighting environment, taking reflection into account.